1. Field of the Invention
Embodiments of the invention relate to a touch sensing system and a method of controlling power consumption thereof.
2. Discussion of the Related Art
User interface (UI) is configured so that users are able to communicate with various electronic devices and thus can easily and comfortably control the electronic devices as they desire. Examples of the user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technologies have continuously expanded to increase user's sensibility and handling convenience. The user interface has been recently developed to include touch UI, voice recognition UI, 3D UI, etc.
The touch UI has been used in portable information appliances and has been expanded to the use of home appliances. A capacitive touch sensing system includes a capacitive touch screen which has durability and definition better than an existing resistive touch screen and is able to recognize a multi-touch input and a proximity touch input. Hence, the capacitive touch sensing system may be applied to various applications. In the touch sensing system, a touch report rate has to increase so as to increase the touch sensitivity a user feels and to accurately recognize a touch input or a dragging trace. The touch report rate is a velocity or a frequency, at which coordinate information of touch data obtained by sensing touch sensors present in the touch screen is transmitted to an external host system.
The capacitive touch sensing system includes a readout integrated circuit (ROIC) and a microcontroller unit (MCU). A touch integrated circuit (IC) is an IC obtained by integrating the ROIC and the MCU into one package. The ROIC includes a driving unit and a sensing unit. The driving unit supplies a driving signal to the touch sensors through lines formed on the touch screen. The sensing unit senses voltages of the touch sensors and detects an amount of changes in the voltages of the touch sensors before and after a touch input. The sensing unit then converts the amount of changes in the voltages into digital data using an analog-to-digital converter (ADC). The MCU analyzes touch raw data converted into the digital data and decides whether or not the touch input is generated. The MCU calculates position coordinates of the touch input.
Because the size of a touch screen used in display devices of small-sized information appliances such as mobile phones and tablet PCs is small, the number of sensing units included in an ROIC of the small-sized touch screen is not many. In the small-sized touch screen, power consumption may be reduced by reducing a driving velocity in an idle state.
A touch screen used in display devices of medium and large-sized information appliances, such as notebook computers, desktop computers, and public displays, includes a large number of touch sensors (or sensor nodes). Because the long lines are used in the medium and large-sized touch screen, a delay of the driving signal increases. Hence, a driving performance and a sensing velocity are reduced. The touch report rate is required to increase so as to increase the touch sensitivity of the user in the medium and large-sized touch screen. A touch sensing system for driving the medium and large-sized touch screen includes a large number of driving units and sensing units of an ROIC. Thus, it is difficult to sufficiently reduce power consumption of the medium and large-sized touch screen using the same method as the small-sized touch screen, i.e., the method for reducing the driving velocity.